1. Field of the Invention
This invention relates to the fabrication of thin film magnetic read/write heads and particularly to a method for forming a slider surface so that the accumulation of lubricant during disk drive operation is reduced.
2. Description of the Related Art
Referring to schematic FIG. 1, there is shown a portion of a hard disk drive (HDD) in which an encapsulated, small thin film magnetic read/write head (30), formed on a ceramic substrate called a slider (7), is used to read and write data on a magnetic medium or storage disk (15). The read/write head (30) is formed using well known semiconductor deposition techniques such as electroplating, CVD (chemical vapor deposition) and photolithographic patterning and etching. The slider (7) has a pre-patterned air-bearing surface (ABS) typically referred to as an ABS plane (300) that faces the rotating disk (15) during HDD operation. The ABS plane (300), shown here in a side view, only defines a vertical boundary of the patterned slider ABS, because the patterning actually incises the plane to create channels for airflow. These channels will be shown in later figures and cannot be seen here. The slider is mounted on the distal end of a head gimbal assembly (HGA) (150) that is activated by an electromechanical mechanism and control circuitry to position the slider-mounted head at various positions along the magnetic tracks on the disk (not shown).
As the disk is rapidly rotated by a spindle motor (not shown), hydrodynamic pressure causes an air flow (arrow, (25)) between the patterned ABS plane (300) of the slider (7) and the surface of the disk (15). This flow lifts the slider so that it literally flies above the surface of the disk at a “fly height” (80), supported on a layer of air. This fly height is approximately 10 nm or less. The edge of the slider into which the disk rotates is called its “leading edge” (200), the opposite edge, which contains the read/write head (30), is called the “trailing edge” (100). The aerodynamics of the slider motion lifts the leading edge higher above the rotating disk surface than the trailing edge.
As disk capacities increase and there are corresponding increases of the area density of the recordings, slider flying height is made to become increasingly lower in order to achieve accurate reading and writing by the head. This reduction in flying height creates a variety of proximity interactions, such as intermolecular forces (IMF), meniscus forces and electrostatic forces (ESF). These forces and the associated influence of disk topography tend to destabilize the aerodynamic motion of the slider. In addition, evidence from various recent slider reliability tests have indicated that the interaction between the slider and lubricants on the disk surface is becoming more critical in determining the stability of the slider's flight over the disk surface. The current negative pressure ABS design has particular geometric surface features that makes the ABS more susceptible to air flow stagnation and even air flow reversal, both of which tends to cause the lubricant on the top surface of the disk to be transferred to the slider's ABS. This occurs even in the absence of any actual contact between the slider surface and the disk surface. Such lubricant transfer contaminates the slider ABS and removes the protective lubricant layer from the disk, which can prevent the slider from flying at optimum design height and further affect the reliability of the hard disk drive (HDD). Therefore, there is a need in the HDD industry to employ an ABS design that can mitigate this transfer of lubricant. The present invention provides such a mitigation of lubricant transfer.
As schematically illustrated in FIG. 2, the surface of the disk (15) is typically covered by an irregular layer of lubricant, which is indicated here as small spherical beads (150). The beads cluster irregularly into small mounds or “moguls” (155). The airflow, indicated by arrow (25), beneath the ABS of the slider creates a distribution of air pressure against the ABS, which is schematically indicated by a curve (160). There is also shown the flow of lubricant (170) to the trailing edge surface (100) of the slider. The flow of lubricant to the trailing edge surface of the slider is a result of the very high air-bearing forces that act on both the ABS of the slider (as indicated by the pressure curve) and on the distribution of lubricant on the disk surface. These forces are instrumental in forming the lubricant moguls (155) as well as the lubricant transfers (170). The detailed causes of the lubricant behavior depend on both the forces and the lubricant properties, such as molecular roughness and cohesion. With the effect of negative pressure ABS design, the majority of the lubricant transferred to the slider is sucked into a trailing air groove (not visible here, but shown as (320) in FIG. 5A) within the patterned ABS of the slider, where it accumulates and resides, because of the sub-ambient pressure within it. Lubricant can also be sheared off to the trailing air groove due to the higher shear on the ABS as it flies near the disk surface.
Referring to FIG. 3, there is schematically shown the illustration of FIG. 2 with additional details to indicate the airflow patterns along the ABS of the slider. Arrow (210) indicates “foreflow,” which is surface flow along the ABS in the direction of the major airflow (arrow (25)) between the ABS and the disk surface. Arrow (220) indicates a region of “backflow” where the surface airflow is counter to the major airflow direction. These two flows also create shear forces (arrows (211), (221)) along the ABS in the two flow directions. In between these two flow regions there is a stagnation region (shown on a lubricant particle (230)) of neither airflow nor shear. As is shown in the figure, lubricant near the trailing edge (TE, (100)) tends to migrate (175) towards the stagnation region. The patterns of lubricant flow will be more clearly indicated when FIGS. 5A and 5B are discussed below.
Although attempts have been made in the prior art to mitigate the effects of lubricant accumulation, these attempts do meet the objects nor provide the properties of the present invention. In this respect, U.S. Pat. No. 7,227,723 (Nath et al) discloses streamline control elements in a recessed area and standing above the recessed area.
U.S. Pat. No. 6,747,847 (Stoebe et al) describes channels located within pads to flush accumulated lubricant.
U.S. Pat. No. 6,356,405 (Gui et al) teaches landing the head at selected stop intervals to remove accumulated lubricant.
U.S. Pat. No. 5,853,959 (Brand et al) states that the invention can create pole patterning features with complex contours to reduce lubricant accumulation, but gives no details.